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758

Appendix: I.

do anything like their share of the "work, so to speak. We pass,
therefore, to the practical principle of

Initial Stressing (during manufacture), by which the outer
rings may be made of greater. assistance. To do this, they are to
be stressed initially in tension, and the inner rings in compression,
and it will be shewn that when the fluid pressure is admitted, the
internal hoop compression will be more than relieved, while the
external hoop tension \vjll be hut slightly increased.

The first and most important method of arriving at the above
result is to build the cylinder in separate concentric tubes, to be
shrunk, the outer over the inner ones.

The tube B, Fig. 748, being shrunk over A, exerts a pressure
between their common surfaces, as shewn on the left at /$, and
this pressure decreases to nothing at the inside and outside of
the cylinder. But such pressure may be likened to a fluid pres-
sure on the inside of B and the outside of A, and it will be easily